1. Field of the Invention
The present invention relates to a metal polishing composition that is used to perform chemical mechanical planarization in a process of producing a semiconductor device and a polishing method therewith.
2. Description of the Related Art
In the development of semiconductor devices typified in large-scale integrated circuit s (hereinafter, referred to as “LSI” in some cases), a method of miniaturization and integration of wirings has been studied to achieve higher integration and higher speed of a semiconductor device. As a technology for realizing this, various technologies such as chemical mechanical polishing (hereinafter, referred to as “CMP” in some cases) have been adopted. The CMP is used to polish a metal thin film used as an interlayer insulating film (SiO2) or a wiring to planarize a substrate or to remove a superfluous metal thin film at the time of forming the wiring (see, for instance, U.S. Pat. No. 4,944,836).
A general method of the CMP is as follows.
A polishing pad is bonded onto a circular polishing platen and a surface of the polishing pad is wetted with a polishing liquid. A surface of a substrate (wafer) is pressed against the polishing pad and predetermined pressure (polishing pressure) is applied from a back surface thereof. In this state, both of the polishing platen and the substrate are rotated. In the CMP, mechanical friction generated by the above operation is used to planarize a surface of the substrate.
As an interconnecting metal, tungsten and aluminum have been generally used in interconnection structures. However, LSIs that use copper lower in wiring resistance than these metals have been developed to achieve higher performance. As a method of interconnecting the copper, a damascene method is known (see, for instance, Japanese Patent Application Laid-Open (JP-A) No. 2-278822). Furthermore, a dual damascene method where a contact hole and an interconnecting groove are simultaneously formed in an interlayer insulating film and a metal is buried in both has come to be widely used. As a target material for copper wiring, high purity copper targets of five nines or more are being shipped.
However, recently, with a demand for higher densification of LSIs, improvement in the electroconductivity and electronic characteristics of copper wirings is demanded to realize miniaturization of wirings. In this regard, use of a copper alloy obtained by adding a third component to high purity copper has begun to be studied.
Furthermore, a high-speed metal polishing method capable of improving the productivity of a high precision and high purity material without causing contamination is in demand. In particular, since copper is a soft metal, when copper or a copper alloy is polished, a phenomenon where only a center portion is polished deeper to form a dish-like dent (dishing), a phenomenon where a plurality of interconnecting metal surfaces forms a dish-like concave portion (erosion) or a polishing scratch is likely to occur; accordingly, a higher precision polishing technology is increasingly in demand.
In recent years, a wafer size has been enlarged to improve the productivity. At present, wafers having a diameter of 200 mm or more are in general use, and wafers having a diameter of 300 mm or more have begun to be produced. With the increase in the size of wafers, the polishing speed difference between a wafer center portion and a wafer peripheral portion tends to be larger. Accordingly, the capability to uniform carry out polishing within the plane of a wafer has begun to be strongly demanded.
On the other hand, a chemical polishing method that depends only on dissolution and does not apply the mechanical polishing method is disclosed for copper and copper alloys (see, for instance, JP-A No. 49-122432). However, since the chemical polishing method polishes depending only on chemical dissolution, a problem of over-polishing a concave portion, that is, dishing, tends to occur in comparison with the CMP which selectively chemically and mechanically polishes a metal film of a convex portion, and accordingly, the flatness is problematic.
In order to overcome the problems in the CMP which uses solid abrasive grains, a metal surface polishing method that uses a combination of a polishing liquid that does not contain abrasive grains and dry etching is disclosed (see, for instance, Journal of Electrochemical Society, 2000, Vol. 147 (10), pp. 3907 to 3913).
When copper wirings are used in the LSI production, a diffusion blocking layer called a barrier layer is generally disposed between a wiring portion and an insulating layer to inhibit copper ions from diffusing to an insulating material. The barrier layer is formed of a barrier material such as TaN, TaSiN, Ta, TiN, Ti, Nb, W, WN, Co, Zr, ZrN, Ru, CuTa alloy, MnSixOy or MnOx, and at least one layer thereof is disposed. The barrier materials themselves have electroconductivity, and accordingly, the barrier material on the insulating layer has to be completely removed to avoid errors such as a leakage current from occurring. In the removing process, a method similar to the polishing of a bulk of a metal wiring material may be applied. This is so-called barrier CMP.
In the bulk polishing of copper, dishing tends to occur in a wide metal wiring portion in particular. Accordingly, it is desirable to be able to control a polishing and removing amount between a wiring portion and a barrier portion so that planarization is ultimately achieved. For this reason, a polishing liquid for polishing the barrier is desired to have appropriate polishing selectivity of copper/barrier metal. Furthermore, since wiring pitch and wiring density are different between wiring layers of the respective levels, it is more desirable to be able to appropriately control the polishing selectivity.
A metal polishing composition that is used in the CMP generally contains solid abrasive grains (such as alumina or silica) and an oxidizing agent (such as hydrogen peroxide or peroxodisulfate). A fundamental mechanism of the CMP that uses such a metal polishing composition is considered to be that the polishing is performed by oxidizing a metal surface with an oxidizing agent and, thereafter, the oxide film is removed with abrasive grains (see, for instance, Journal of Electrochemical Society, 1991, Vol. 138 (11), pp. 3460 to 3464).
A metal polishing composition containing peroxodisulfate is characterized in being capable of obtaining a high polishing speed. However, there is a problem in that dishing and erosion are likely to proceed. As one measure to overcome the dishing, benzotriazoles are added to a metal polishing composition as an anti-corrosion agent that inhibits a metal film from being polished (see, for instance, JP-A No. 2005-116987). According to the method, a protective film is formed on a metal film of a semiconductor base material, and accordingly, while convex portions are removed by abrasive grains, the metal film is left in concave portions, whereby a desired conductor pattern is obtained. The protective film in the concave portions inhibits the dishing from occurring, and accordingly, high flatness is obtained. However, in the CMP, the erosion caused by eroding of the barrier film is not inhibited from occurring even when a metal polishing composition that uses an anti-corrosion agent that can obtain high flatness is used. That is, there is the demand for the flatness necessary for producing devices to be further improved.